The present invention relates to an arrangement for orienting the magnetization direction of thin layers on plate-form substrates with a substrate mounting for at least one substrate, which defines a positioning plane for the at least one substrate, and in which, on one side of the positioning plane, a magnet arrangement is provided; such according to the claims.
The invention relates further to a vacuum coating installation a substrate with at least one magnetic layer method for the production of substrates as well as use of the arrangement.
In the production of magnetic layers, for example by cathode sputtering, it is often desirable to generate in these layers a magnetic anisotropy, which has a nominal distribution within and along the layer. As the nominal distribution especially frequently a uniaxial, i.e. collinear magnetic anisotropy is required, whose direction is defined with respect to the substrate.
By collinear anisotropy or collinear anisotropy distribution should be understood a magnetic anisotropy, which is directed uniformly along a considered layer domain. In this sense it is also possible to speak of a xe2x80x9chomogeneity of the anisotropyxe2x80x9d.
Normally only small angular deviations of the anisotropy direction from the predetermined direction are permitted. Such an anisotropy in the magnetic layer is attained thereby that during the substrate coating a correspondingly directed or oriented magnetic field in the coating regions is brought into effect. After the coating the magnetic anisotropy in this case has the direction of the previously applied field.
It is known from DE-OS 196 43 841 to dispose substrates radially offset and distributed about the center on a substrate holder and to coat them in this disposition with a magnetic material. In this process the substrate holder is rotated about the central axis. Beneath the positioning plane for the substrates defined by the substrate mountings on the holder, radially oriented with respect to the central axis, is provided a stationary electromagnet with coil and yoke, which latter generates immediately under the positioning plane a magnetic field directed substantially radially to the central axis. This approach is of disadvantage under various aspects:
If larger substrates are to be coated, due to the disposition, which perforce is eccentric, and substrate holder rotation, the holder arrangement is extraordinarily large and mechanically expensive. The holder size has a disadvantageous effect on the coating rate, for example by means of sputter sources.
The production of substrates with multilayer coating systems of optionally differing magnetic materials connected with the requirement to realize in the differing magnetic layers different anisotropy distributions, in particular directions, cannot be realized with this known arrangement with exclusively radially directed magnetic fields, unless the substrates are repositioned in order to realize different anisotropy directions on different substrate layers.
U.S. Pat. No. 5,630,916 discloses providing beneath a positioning plane for substrates an electromagnet which extends far beyond the dimensions of the substrate. In order to generate collinear field lines in the substrate region, the dimension of the electromagnet must be markedly greater than the substrate dimension. Here also, there is no capability of impressing in the case of multilayer coatings on the substrate onto the discrete magnetic layers differing anisotropy distributions, in particular directions, without for this purpose geometrically rotating the substrate between the individual coating steps. As in all arrangements for magnetic field generation in the substrate region in which a closed yoke plate optionally with coils beneath the substrate plane is available, a further disadvantage comprises that it is difficult or impossible to bring to the substrate mechanical devices, for example for the substrate movement from below. But such devices are often required in modern coating installations, for example for the substrate transport. Similar problems are encountered if the substrate is to be cooled or heated from below or also for applying measuring instruments.
From DE-OS 43 12 444 is known a procedure, similar to that described in connection with DE-OS 196 43 841, in which the distance can be set between a radially disposed permanent magnet and the substrate eccentrically and rotationally supported.
EP-A-0 435 838 discloses providing coaxially to a substrate holder a polygonally wound, planar coil, with which on the centrally supported substrate a radial magnetic anisotropy is attained. The disadvantages already listed above essentially apply also to this arrangement.
From EP-A-0 584 768 is further known to generate a uniaxial anisotropy with small angular deviations on magnetically coated rectangular substrates thereby that parallel rod magnets are disposed laterally beneath the substrate. Here also a changing between nominal anisotropy distributions is not possible except, as in the previously described known procedures, through the mechanical rotation of the magnet arrangement with respect to the substrate, which can only be realized with considerable expenditures.
The present invention addresses the problem of proposing an arrangement or a coating installation or a production method, by means of which:
in simple manner a desired nominal anisotropy distribution can be realized on at least one magnetic layer of a substrate. In particular for the vacuum coating of a substrate with a low retentivity layer, the desired nominal anisotropy distribution is to be an anisotropy collinear in a predetermined direction;
without mechanical change of the relative position of substrate and magnet arrangement are to be realizable several low retentivity layers provided on a substrate with different anisotropy distributions, in particular directions, thereby that the anisotropy distribution or direction to be attained can be set in simple manner;
large-area substrates are to be imparted with desired magnetic anisotropy distribution, in particular with a collinear predetermined or predeterminable direction. More especially, in the case of large-area substrates with said layers, a very good collinearity of the anisotropy direction is to be attained at least to a high degree in the entire substrate region.
This problem is solved on the arrangement according to the invention where the magnet arrangement comprises at least three electromagnets, whose dipole axes are at least approximately parallel to the positioning plane and, viewed perpendicularly to the positioning plane, define a closed surface. It becomes thereby possible by superposition of the fields of the electromagnets and corresponding dimensioning and orientation of their dipoles, to realize in the positioning plane or in the corresponding magnetic layer of a substrate held on the substrate mounting, a desired resulting field line pattern or a nominal anisotropy direction distribution, and to switch it over extremely simply, for example for the imparting of a second layer, as will yet be explained.
In a preferred embodiment of the arrangement according to the invention the dipole axes are in a plane parallel to the positioning plane. They further, preferably additionally, define a regular n-polygon, and further preferred, more than three electromagnets are provided with n being the number of electromagnets.
In particular in view of the requirement to realize on said layers a homogeneous distribution of the anisotropy direction within maximally large regions of the layer, but, as previously, to be able to change this anisotropy with respect to its direction in extremely simple manner, it is proposed that an even number of electromagnets is provided, preferably a number divisible by 4, wherewithxe2x80x94as will yet be explainedxe2x80x94the electromagnets, grouped in quadrants, can be optimally set and reset with respect to their dipole directions and dipole strengths with the utilization of symmetries.
In a further preferred embodiment the magnet arrangement comprises two electromagnet groups, on which the electromagnets generate dipoles directed as follows:
The dipolesxe2x80x94in the sense of vector componentsxe2x80x94have a first component, parallel to the positioning plane and in a first direction, which are directed uniformly on the electromagnets of both groups.
The dipoles have second components, parallel to the positioning plane and perpendicular to the first direction, which are directed on one group inversely to those of the second group, thus pointing in compensating directions between the groups.
Furthermore, in a preferred embodiment the electromagnets are formed by coils, which are wound on a common magnet core enwrapping said surface, therein preferably on a common toroidal core.
The calibrating of the dipole magnitudes or values at the electromagnets in a first embodiment takes place by providing coils which have at least partially different winding numbers.
The electromagnets are furthermore connected to current generators, which charge them with DC and/or AC and/or DC with superimposed AC current. If AC current is employed, optionally in superposition with DC current, then preferably with a frequency f, to which applies:
1 Hzxe2x89xa6fxe2x89xa6100 Hz. 
Instead of, or supplemental to, the setting of the dipole magnitude on the provided electromagnets by providing coils of different winding numbers, a second embodiment proposes that at least one portion of the electromagnets is connected to current generators, which charge the electromagnets with currents, to which applies:
the DC current values are different and/or
the AC current amplitudes and/or phases are different.
Consequently, with a provided set of electromagnets the desired anisotropy distribution, in particular the desired anisotropy direction, can be attained by the redirecting of the currents acting upon the electromagnet coils.
Therefrom follows directly a further preferred embodiment of the arrangement according to the invention, in which the electromagnets are connected to a current generator arrangement, at which the distribution of output currents to the electromagnets can be switched over into at least two differing distribution states. It is understood that it is possible to define more than two current distribution states and to redirect the anisotropy direction virtually in any desired direction from 0xc2x0 to 360xc2x0 in the positioning plane. By distribution of the output currents of the generators are understood the distribution of DC values or AC amplitudes or mutual phase position of the currents as they are generated at a predetermined set of electromagnets.
If coils of the electromagnets are wound on a common toroidal core, preferably an even number of coils, in particular a number divisible by 4, and if a plane of symmetry, which contains the axis of the toroidal core, divides the coils into two groups, with direction components of the dipoles of the coils of both groups being directed uniformly in the direction parallel to said plane of symmetry, the strength of the dipoles is preferably selected at least approximately proportional to a cos xcfx86 function, wherein xcfx86 is the polar position angle of the particular coil with respect to the axis of the toroidal core.
If therefore one follows along the coils of a group around the toroidal core, as stated the values of said dipoles are preferably laid out according to said cos xcfx86 function. Thereby the circular arrangement of the coils is taken into consideration, in view of the generation of a resulting collinear anisotropy. The anisotropy direction is obtained in the direction of the line of intersection of said plane of symmetry with the positioning plane.
It is now readily evident that by switching-over the distribution of the currents flowing through the coils, the angular position of said plane of symmetry is pivotable about the toroidal core axis into predetermined angular positions and/or is freely selectable, preferably in steps, in the range from 0xc2x0 to 360xc2x0.
For while the electromagnets are stationary, as is also the substrate on the positioning plane, through the current-directed redefinition of said plane of symmetry an adjustment is obtained of the resulting anisotropy direction in the positioning plane or on the substrate.
In order to be further able to change rapidly from one preferred nominal anisotropy distribution or direction to another, in particular from the generation of a collinear anisotropy in a first direction to the generation of a collinear anisotropy in another and in order to herewith generate for example in two magnetic layers of a substrate, first, a collinear anisotropy in the one, subsequently in the second layer in a second direction, for example rotated by 90xc2x0, it is proposed that at least two of the magnet arrangements are provided, each of which is operated selectively.
In addition to the above described thereby a further feasibility for the direction switching of the anisotropy direction results, according to which this change is carried out on one and the same electromagnet set by redirecting the dipole-generating currents. It is understood that it is readily possible to provide optionally two or more of said magnet arrangements, to operate these alternatively or optionally even together and, in addition, to set or redirecting the currents generating the dipole on the electromagnets of said magnet arrangements.
In a preferred embodiment of the arrangement according to the invention with two of the magnet arrangements, it is proposed that the magnet arrangements are disposed coaxially with respect to an axis perpendicular to the positioning plane, and are preferably identical, but with respect to this axis are rotated mutually about an angle of preferably 90xc2x0. Thereby, in particular in the case of the above defined plane of symmetry on a toroidal core, by each of the magnet arrangements a plane of symmetry is defined, which are oriented differently, as stated, preferably form a 90xc2x0 angle. Thereby the capability is obtained of redirecting by 90xc2x0 the resulting field direction or anisotropy direction in simple manner in one switch-over step.
An extremely compact structure, in which additionally identical conditions obtain with respect to the positioning planes for both magnet arrangements, is attained thereby that coils of both magnet arrangements are wound on the same core, preferably a toroidal core.
On the arrangement according to the invention the substrate mounting is preferably developed for receiving at least one plate-form substrate, which is preferably rectangular or, and especially preferred, circular. However the substrate mounting can quite well be developed for receiving several plate-form substrates. But, in any event, the magnet arrangement or the two or more magnet arrangements are preferably disposed symmetrically to a center axis through the substrate mounting. If the substrate mounting is developed for receiving one substrate, this is provided on the mounting centered with respect to said center axis, if several substrates are provided on the mounting, then analogously about said axis centered in groups.
Since with the arrangement according to the invention in said positioning plane a collinear field line pattern over a large area can be realized and therefrom correspondingly over a large area a collinear anisotropy distribution on the layer(s) of a substrate, in a preferred embodiment the substrate mounting can be developed for receiving at least one plate-form substrate with a maximum diameter of at least 100 mm, preferably of at least 150 mm, preferably even of 200 mm or even of 300 mm.
The arrangement according to the invention in the preferred embodiment in and along said positioning plane of the substrate mounting, in particular along areas corresponding to the listed substrate dimensions, generates a magnetic field with collinear field lines which deviate at most xc2x15xc2x0, preferably at mostxc2x13xc2x0, preferably even at most xc2x12xc2x0 from the ideal collinearity or parallelity.
A coating installation according to the invention is also distinguished. For the reception of at least one substrate to be coated in the coating chamber it comprises an arrangement of the above described type. In a preferred embodiment the coating installation in the chamber comprises at least one sputter source with a target of a magnetic, preferably low retentivity material.
A substrate according to the invention with at least one magnetic layer is distinguished as well. The substrate according to the invention in a preferred embodiment comprises at least two magnetic layers each with said magnetic anisotropy preferably in different directions.
The method according to the invention is furthermore distinguished according to other claims.
With the procedure according to the invention not only magnetic anisotropies can be generated which are highly exactly collinear and over a large area in magnetic substrate layers, but rather additionally the direction of this anisotropy can be changed extremely simply such that on substrates with two and more magnetic layers, each in different directions, collinear anisotropies can be generated without repositioning the substrates during the coating process.
The demand for such substrates with collinear anisotropies shifted by 90xc2x0 exists for example in the production of magnetic sensors, such as are utilized in so-called thin-layer heads for fixed disks, in the field of sensory analysis of the motor vehicle field and in so-called MRAMs (Magnetic RAM, see for example Hubert Brxc3xcckl xe2x80x9cNon-Volatile Memoryxe2x80x9d, Magnetic Storage Industry Sourcebook, 1999). Furthermore said demand is also made in the production of multilayer coating systems, which are structured according to the principle of xe2x80x9cspin valvexe2x80x9d (see B. Ocker, W. Maass et al., xe2x80x9cSpin Valves for High Densityxe2x80x9d, Magnetic Storage).
A further application of the invention is for the magnetic measurement techniques, in which for example the magnetic properties of magnetic layers or materials are measured. In these measurements it is in many cases necessary to apply collinear homogeneous magnetic fields in different directions onto the samples to be measured.
The procedure realized according to the invention in the above connection is consequently according to the use according to the invention suitable for all application purposes in which in a specific plane over a large area a specific magnetic field distribution is desired, especially again a homogeneous collinear field distribution over relatively areal domains, and for this purpose said plane is defined instead of the above described positioning plane.